i) Field of the Invention
The present invention relates to an array antenna mounted on spacecrafts.
ii) Description of the Related Arts
Conventionally, for a satellite communication, a radio wave research or the like, an array antenna is used by mounting on a spacecraft or an artificial satellite. For example, in "Japanese Earth Resources Satellite-1 Synthetic Aperture Radar", Nemoto et al., Proceedings of the IEEE, Vol. 79, No. 6, pp. 800-809. June, 1991, an array antenna mounted on spacecrafts is disclosed, as shown in FIGS. 14 to 17.
In FIG. 14, there is shown an arrangement of electrodes on the back of an extended array antenna 9. In the drawing, 8 (in general, a plurality number of) subarrays 1 each have a flat plate form. In this case, the 8 subarrays 1 aligned in the transverse direction are successively connected with one another via joint parts 2. In such a connection structure, the array antenna 9 can be stowed, as shown in FIG. 17A, and be extended, as shown in FIG. 17C.
Each subarray 1 is provided with a subarray feeder 3. The subarray feeder 3 is formed, as shown in an enlarged scale in FIG. 15B. In FIG. 15B, the subarray feeder 3 is formed on the back of a support 6 in a pattern so as to feed to antenna elements 7 mounted on the surface of the support 6. In this conventional case, as shown in FIG. 15A, 8 antenna elements 7 are provided for each subarray 1.
Each subarray feeder 3 is connected to an intersubarray feeder 4 and the intersubarray feeder 4 is coupled with an RF (radio frequency) signal feeding cable 5. As a result, a circuit construction shown in FIG. 16 can be obtained. As shown in FIG. 16, a signal output from a transmitter 10 within a spacecraft body 8 is fed to each subarray feeder 3 via the RF signal feeding cable 5 and the intersubarray feeder 4. A feeding amplitude and a phase can be adjusted in the intersubarray feeder 4 and each subarray feeder 3. From each antenna element 7, a radio frequency signal is irradiated depending on the feeding. In this case, when the array antenna 9 is used for receiving a signal, the transmitter 10 is replaced with a receiver.
In the array antenna 9 having the connection structure shown in FIG. 14, mounted on the spacecraft, the array antenna 9 is stowed in a position along the surface of the spacecraft body 8 when the spacecrafts is launched. After the launching, the array antenna 9 is rotated 90 degrees in an outer space, as shown in FIG. 17A. From this state, by functioning the joint parts 2, the array antenna 9 is extended to the left and right hand sides from a center arm 11, as shown in FIG. 17B, to become the flat plate form, as shown in FIG. 17C. The center arm 11 has a function for supporting the array antenna 9 on the spacecraft body 8.
While the array antenna 9 is extended, the attitude of the spacecraft body 8 is adjusted or the attitude (angle) of the array antenna 9 with respect to the array antenna 9 is adjusted so as to direct a directivity beam of the array antenna 9 to the desired direction. Further, the shape of this beam can be determined by adjusting the feeding amplitude and the phase for each subarray 1 (more specifically, the antenna elements 7).
However, the control of the direction and the shape of the directivity beam can be carried out only when the array antenna 9 is completely extended in the flat plate form. Also, the extended state in the flat plate form of the array antenna 9 must be continuously maintained in the outer space beyond the reach of hands. Hence, the coupling between the subarrays 1 by the joint parts 2 must be very much strong. As a result, the volume of the joint parts 2 becomes large and the weight of the same also becomes heavy. Further, when the flat plate form of the subarrays 1 or the array antenna 9 is changed or deformed due to the secular change, the direction and the shape of the beam are shifted from the initials. However, since the array antenna 9 is mounted on the spacecraft beyond the reach of the human's hands, it is quite difficult to correct the shifts.
Further, it is necessary to change the attitude of the spacecraft body 8 or the attitude (angle) of the array antenna 9 with respect to the spacecraft body 8. This restricts the degree of freedom of the attitude of the spacecraft body 8.